The present invention relates to vehicle navigation, and more particularly concerns avoidance of terrain and hazardous conditions.
Avoidance of terrain and other hazards has been an active field of development for a number of decades. Both military agencies and commercial establishments continue to investigate improved methods for increasing the safety of flights against the possibility of CFIT (xe2x80x9ccontrolled flight into terrainxe2x80x9d) accidents. There is also a need, particularly for airlines, for improved methods of tracking weather systems with respect to prearranged flight plans from dispatchers.
Military terrain-avoidance systems appeared in the 1960s. A downlooking active radar system measured proximity to local terrain and maintained a specified ground clearance. Some designs included an automatic control loop controlled the aircraft""s pitch, maintaining clearance by climbing over obstacles detected by the radar. Other designs provided a display for manual control by the pilot. R. L Kisslinger et al., xe2x80x9cManual Terrain-Following System Development for a Supersonic Fighter Aircraft,xe2x80x9d Journal of Aircraft, Vol. 3, No. 4 (July-August 1966) describes an example..
Similar avoidance systems for civilian aircraft followed a few years later, after radar altimeters were introduced into commercial transports. The altimeter provided an alert upon encountering a preset minimum height above local terrain. D. Bateman, xe2x80x9cDevelopment of Ground Proximity Warning Systems (GPWS),xe2x80x9d Royal Aeronautical Society Conference on Controlled Flight into Terrain, London, Nov. 8, 1994, describes an early system of this kind. This and other examples are found in U.S. Pat. No. 3,936,796 (Bateman), U.S. Pat. No. 3,944,968 (Bateman et al.), U.S. Pat. No. 3,946,358 (Bateman), U.S. Pat. No. 3,947,809 (Bateman), U.S. Pat. No. 4,030,065 (Bateman), U.S. Pat. No. 5,220,322 (Bateman), and U.S. Pat. No. 5,410,317 (Ostrum et al.).
Later, military agencies developed onboard stored terrain data bases for aiding inertial navigation systems in cruise missiles and for displaying real-time terrain to aircraft pilots. J. Stone, xe2x80x9cThe Potential for Digital Databases in Flight Planning and Flight Aiding for Combat Aircraft,xe2x80x9d NATO document AGARD-AG-14, June, 1990 describes this concept. Digital map computers provide perspective terrain views with overlays of flight plans and of mission and threat data for current fighter aircraft, as exemplified in U.S. Pat. No. 5,086,396 (Waruszewski), U.S. Pat. No. 5,264,848 (McGuffin), U.S. Pat. No. 5,371,840 (Fischer), U.S. Pat. No. 5,406,286 (Tran et al.), U.S. Pat. No. 5,504,686 (Lippitt et al.), and U.S. Pat. No. 5,526,620 (Kodet et al.).
More recently, commercial systems combined terrain databases with radar sensors to provide a situational display. These systems also incorporate look-ahead algorithms to calculate an aircraft""s future location from its present position and velocity vector, and can warn a pilot up to 20 to 60 seconds ahead of an impending loss of adequate terrain clearance. Referred to as TAWS (xe2x80x9cterrain awareness and warning systemsxe2x80x9d), some of these products are described in U.S. Pat. No. 4,646,244 (Bateman), U.S. Pat. No. 5,414,631 (Denoize et al.), U.S. Pat. No. 5,488,563 (Chazelle et al.), U.S. Pat. No. 5,638,282 (Chazelle et al.), U.S. Pat. No. 5,677,842 (Denoize et al.), U.S. Pat. No. 5,798,712 (Coquin), and U.S. Pat. No. 5,839,080 (Muller et al.).
Even the most recent systems, however, are limited by their lack of ability to predict aircraft course and altitude. Extrapolation cannot anticipate course and altitude changes and other maneuvers as an aircraft follows its flight plan.
Flight plans for commercial transports are often prepared hours before departure. Although they are checked for hazards at the time, a trend toward user-defined trajectories and dynamic rerouting create a need for an on-board capability for continuing to check the entire flight plan for hazards during a flight.
The present invention offers a capability for finding conflicts with terrain and other hazards over an entire predicted flight plan, rather than for only a short time into the future. It can be implemented relatively inexpensively, and requires no additional infrastructure. It can be easily extended to modeling hazards other than terrain, including moving hazards such as weather.
The invention determines whether a predicted plan or trajectory intersects with terrain features or other hazards by modeling it as a dimensioned volume, comparing the volume with a model of the appropriate terrain or other hazard, and reporting any intersection with the trajectory volume. Dangerous situations can be communicated directly in real time to the aircraft crew or other persons. Other significant aspects of the invention can employ a hierarchical intersection determination, constrained-optimization techniques, and moving-hazard tracking.
The invention is not inherently limited to aircraft, and may also find utility in, for example, submarine navigation, trip planning for other vehicles. Potential applications exist in fields such as robotics, for ensuring that robots remain clear of each other and of other obstacles. That is, the terms xe2x80x9cplanxe2x80x9d and trajectoryxe2x80x9d should be given a broad umbra. Also, the term xe2x80x9chazardxe2x80x9d must be taken broadly to include other types of features to be avoided, or even perhaps to be sought out or approached in some cases.